Technical Field
The present disclosure relates generally to the processing or purifying of hydrocarbon feedstocks. More specifically, the present disclosure relates to a process for reducing a bromine index of a hydrocarbon feedstock, for example an aromatic hydrocarbon feedstock, via an adsorption process or technique.
Description of the Related Art
Hydrocarbon feedstocks, for example aromatic hydrocarbon feedstocks, are commonly derived from various petrochemical processes such as naphtha reforming and thermal cracking (pyrolysis). Aromatic hydrocarbon feedstocks are commonly used in a variety of petrochemical and industrial processes. For example, aromatic hydrocarbon feedstocks that contain benzene, toluene, and xylene (BTX), and heavy aromatic streams (e.g., with hydrocarbons having at least 9 carbon atoms), are often used in the production of para-xylene.
However, aromatic hydrocarbon feedstocks often contain contaminants, for instance bromine-reactive compounds such as unsaturated hydrocarbons (e.g., olefins such as mono-olefins and multi-olefins, diolefins, and styrenes), which can cause undesirable side reactions in downstream processes. Traces of olefins can also form gums and undesirable byproducts, which can coat the heat transfer surfaces of reaction or operating systems, and hence reduce the efficiency of said reaction or operating systems.
Accordingly, said contaminants should be removed from the aromatic hydrocarbon feedstocks before the aromatic hydrocarbon feedstocks are used for the various petrochemical and industrial processes.
A conventional method for measuring levels of unsaturation or contamination of hydrocarbons, for example aromatic hydrocarbons, is via the bromine index (BI). Typically, the bromine index (BI) of an aromatic hydrocarbon reflects the level of unsaturation, and hence contamination, of the aromatic hydrocarbon. The measurement of the bromine index (BI) in an aromatic hydrocarbon can be done via the method described by ASTM D 5776-99, the entire contents of which are incorporated herein by reference. Specifically, the bromine index (BI) is defined as the number of milligrams of bromine consumed by 100 grams of hydrocarbon sample under the required conditions. This is to say, the bromine index (BI) of a hydrocarbon sample can be defined as the number of milligrams of bromine that will react with unsaturated hydrocarbons (e.g., olefins) that are present in 100 grams of said hydrocarbon sample.
There are numerous existing methods or techniques for reducing the bromine index (BI) of hydrocarbon feedstocks (e.g., aromatic hydrocarbons feedstocks). Removal of unsaturated hydrocarbons, for example olefins, from aromatic hydrocarbon feedstock has been commercially performed using alkylation, polymerization, and oligomerization processes, which are catalyzed by hydrotreating catalysts and/or acid clay catalysts. The alkylation, polymerization, and oligomerization processes typically require multiple processing units or equipment units, for example a catalytic unit for the alkylation, polymerization, and oligomerization processes, and a separation unit for the distillation or extraction of formed products. Accordingly, with such existing processes, capital investment to build or obtain the multiple processing units or equipment units is required.
Said catalysis occurs between the unsaturated hydrocarbon molecule (e.g., olefin molecule) and the catalyst (e.g., clay catalyst), and results in formation of heavy molecule hydrocarbons as a by-product. Accordingly, processes for removing said heavy molecule hydrocarbon by-products are required before further fractionation, processing, or utilization of the aromatic hydrocarbon feedstock.
In addition, due to the formation of heavy molecule hydrocarbons, used catalysts generally have to be regenerated with oxidative agents for removing coke. This regeneration process is described in United States patent applications of publication numbers US 20060270886 and US 20070112240. For ensuring complete coke removal, said regeneration process has to be performed at a significantly high temperature. Furthermore, a rejuvenation process using a reductive or reducing agent is typically required. The need for high temperatures during the regeneration and rejuvenating processes adds to the overall or total costs associated with existing processes for removing contaminants such as unsaturated hydrocarbons from aromatic hydrocarbon feedstocks.
More recently, zeolites have been proposed as replacement for clays in the removal of bromine reactive contaminants such as unsaturated hydrocarbons (e.g., olefins) from aromatic hydrocarbon feedstocks. Methods or techniques for removing bromine reactive contaminants from aromatic hydrocarbon feedstocks with the use of zeolites have been disclosed and described in several patent documents.
For example, U.S. Pat. No. 6,368,496 discloses a method for removing bromine reactive contaminants from an aromatic hydrocarbon stream, the method including contacting the aromatic hydrocarbon stream with an acid-active catalyst composition under specific pressure and temperature conditions. U.S. Pat. No. 6,781,023 discloses a catalytic method for removing bromine reactive contaminants from an aromatic hydrocarbon stream, the method comprising providing the aromatic hydrocarbon feedstream and contacting the feedstream with an unbound or self-bound MCM-22 under specific pressure and temperature conditions.
In most industries, including the petrochemical and chemical industries, profit margins and safety are important considerations. Accordingly, there remains a need for alternative, for instance, more cost-effective, safer, and/or efficient methods and techniques for removing contaminants, for example bromine-reactive contaminants such as unsaturated hydrocarbons, from hydrocarbon feedstocks or aromatic hydrocarbon feedstocks, and correspondingly reducing the bromine index (BI) of said hydrocarbon feedstocks or aromatic hydrocarbon feedstocks.